In December 1922, companion bills calling for 50-cent pieces "in commemoration of the one hundredth anniversary of the enunciation of the Monroe Doctrine" were introduced in the House and Senate. The Senate bill was introduced by Senator Hiram Warren Johnson (R-CA); Representative Walter Franklin Lineberger (R-CA) introduced the House bill.
The bills proposed the coining of 300,000 silver 50-cent pieces of standard specifications. The bills allowed for the coins to be struck at multiple US Mint facilities without an expiration date. No restrictions on the year to be placed on the coin were included, nor were any ordering parameters by which the Los Angeles Clearing House (the coin's sponsor) had to abide. A multi-year program with coins struck at Philadelphia, Denver and San Francisco was a legal possibility!
Upon introduction, Senator Johnson's bill was referred to the Senate Committee on Banking and Currency; Representative Lineberger's bill was referred to the House Committee on Coinage, Weights, and Measures. The Senate Committee moved quickly and reported its bill favorably and without amendment. The House Committee held a Hearing on the coin proposal, and took the same action as the Senate Committee a few days later.
The Senate passed its version of the bill via Unanimous Consent and sent it to the House for concurrence. When the House brought up its version of the bill for consideration, it substituted the Senate bill for its own and passed it without issue.
The bill was then examined and signed in each chamber, at which time it was submitted to the President for approval. US President Warren G. Harding signed the bill into law on January 24, 1923.
1923 Monroe Doctrine Enunciation Centennial Half Dollar

For more on the history of the Monroe Doctrine half dollar and discussions of its interesting design, check out:
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1923 Monroe Doctrine Centennial-
1923 Monroe Doctrine Centennial - Ancestors-
1923 Monroe Doctrine Centennial - Coins with Hands Thread - Design Controversy
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1923 Monroe Doctrine Centennial - Coins with Flora Thread-
1923 Monroe Doctrine Centennial - Coins with Conjoined Portraits ThreadFor other of my posts about commemorative coins and medals, check out:
Commems Collection